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The Single UNIX &reg; Specification, Version 2<br>
Copyright &copy; 1997 The Open Group

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<h4><a name = "tag_000_001_221">&nbsp;</a>NAME</h4><blockquote>
atan2 - arc tangent function
</blockquote><h4><a name = "tag_000_001_222">&nbsp;</a>SYNOPSIS</h4><blockquote>
<pre><code>

#include &lt;<a href="math.h.html">math.h</a>&gt;

double atan2(double <i>y</i>, double <i>x</i>);
</code>
</pre>
</blockquote><h4><a name = "tag_000_001_223">&nbsp;</a>DESCRIPTION</h4><blockquote>
The
<i>atan2()</i>
function computes the principal value of the arc tangent of
<i>y/x</i>,
using the signs of both arguments to determine the quadrant of
the return value.
<p>
An application wishing to check for error situations should set
<i>errno</i>
to 0 before calling
<i>atan2()</i>.
If
<i>errno</i>
is non-zero on return, or the return value is NaN,
an error has occurred.
</blockquote><h4><a name = "tag_000_001_224">&nbsp;</a>RETURN VALUE</h4><blockquote>
Upon successful completion,
<i>atan2()</i>
returns the arc tangent of
<i>y/x</i>
in the range [-, ] radians.
If both arguments are 0.0, an implementation-dependent value is returned and
<i>errno</i>
may be set to [EDOM].
<p>
If
<i>x</i>
or
<i>y</i>
is NaN, NaN is returned and
<i>errno</i>
may be set to [EDOM].
<p>
If the result underflows, 0.0 is returned and
<i>errno</i>
may be set to [ERANGE].
</blockquote><h4><a name = "tag_000_001_225">&nbsp;</a>ERRORS</h4><blockquote>
The
<i>atan2()</i>
function may fail if:
<dl compact>

<dt>[EDOM]<dd>
Both arguments are 0.0
&nbsp;or one or more of the arguments is NaN.

<dt>[ERANGE]<dd>
The result underflows.

</dl>
<p>
No other errors will occur.
</blockquote><h4><a name = "tag_000_001_226">&nbsp;</a>EXAMPLES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_001_227">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_001_228">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_001_229">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="atan.html">atan()</a></i>,
<i><a href="isnan.html">isnan()</a></i>,
<i><a href="tan.html">tan()</a></i>,
<i><a href="math.h.html">&lt;math.h&gt;</a></i>.
</blockquote><h4>DERIVATION</h4><blockquote>
Derived from Issue 1 of the SVID.
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UNIX &reg; is a registered Trademark of The Open Group.<br>
Copyright &copy; 1997 The Open Group
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